Project: Gen3 JDM Integra Si-VTEC
The JDM Honda Integra changed generation in early 1993. The new
model, coded DB for 4-door and DC for 3-door received a body revision and
quad-projector headlights. The most significant change however was the engine
upgrade, from the 1.6l B16A to a longer stroke 1.8l DOHC VTEC B18C with a new
intake manifold. The B18C engine red-lines at 8000rpm and generates 180ps at
7600rpm. Although only 10ps higher than the current B16A, its bigger
displacement and the special intake manifold gave much better low-end and
mid-range making it more driveable over the B16A especially with curb weight
being only moderately increased.
The new B18C intake manifold uses two sets of intake runners. The cut-away
diagram of this intake manifold on the right shows how the runners are arranged.
A marks the plenum (which the throttle body attaches to).
B is where the intake runners attaches to the cylinder head.
C is used to give readers a sense of perspective, it marks the
fuel injectors. The top set of runners are curved around the lower set making it
longer. The lower set of runners have butterfly valves built into them (marked
by D). During low and mid-rpm operations, the valves are closed
and only the top set of runners are feeding air into the cylinders. After
5800rpm, the butterfly valves open and air will now be fed into the cylinders
via both sets of intake runners. This new intake system works in conjunction
with VTEC, which now switches at 4400rpm, to optimize air-flow into the
cylinders at all RPMs making the power/torque curve of the B18C extremely wide
and flat. Peak torque of the B18C is 17.8kgm at 6200rpm but torque output of the
B18C is already near or at 17.0kgm all the way from approx 2500rpm right until
the 8000rpm, a smaller than 5% spread for practically all operating RPMs !!
Power-upgrade to the B18C
The DC2 Integra in this article is a JDM used-import. Manufactured in 1993,
it is around 6 years old when the owner decided to upgrade its overall
performance last year in 1999. The approach he took was the interesting question
of using only drop-in/straight-fit mods. Drop-in/straight-fit mods are designed
to give instant power increase with minimal work needed. Often it takes no more
than an hour or so visit to the proper speed shop for dismantling and fitting.
Straight-fit mods are designed so that they utilize the original mounting points
and will not require any sawing or hacking for fitting.
Technically drop-in mods exploits the head-room and compromises built into a
stock engine. Head-room is typically safety factor intentionally built-in, eg
running the engine slightly rich to compensate for varying atmospheric
conditions. Compromises are usually built-in for legal requirements or for
domestic desirability : emissions, noise, fuel consumption, driveability, and
sometimes even manufacturing cost. Drop-in mods - if properly designed - can
exploit these two factors, eg by fine-tuning the air-fuel ratio, for instant
power-gains without too much engine work. The down-side is that for
well-designed engines - and Honda's DOHC VTEC engines are prime examples - the
head-room is smaller and the compromises are more performance oriented, so power
gains will almost always be only moderate. Also exploiting the compromises means
some sacrifices for the driver, eg much louder exhaust, or in some cases the
ethical issue of increasing emissions.
Prior to his product purchases, the owner did extensive research in the
Internet as well as consulted with friends & speed shops. For the engine, he
decided on the complete filter-cat/back-header-a/f regulator combination. He
also wanted to properly tune the a/f regulator device so a dyno session was
deemed necessary. This combination was an almost complete straight bolt-on
except for one minor detail which we will cover later. Careful planning was done
so that the main hardware; headers and cat-back were installed first. These were
bought from one shop. The remainder items, the air-filter, a/f regulator and
dyno-tuning were from another shop which also supplied all the rest of his
The first item that went in were Tanabe headers. This is a
stainless steel design optimized for power delivery. The headers were for the
B18C Spec-R since Tanabe doesn't make headers for the regular B18C. The
Tanabe G-Medallion cat-back exhaust system was installed the
following day. However the B18C Spec-R uses a shorter cat so the headers
extended longer. When used with the longer cat of the B18C, the cat-back exhaust
was pushed further back causing some of the mounting brackets to hit the
under-carriage. This was resolved by replacing the cat with a custom made
straight-through pipe. Though the owner was concerned about the increased
emissions, the was unfortunately his only immediate solution.
During the weekend, the final parts were installed. This comprises the
installation of a HKS Super-Power-Flow system, ie the
Super-Power-Flow air-filter plus a custom designed HKS extension pipe and
mounting brackets. This kit places the filter in the optimum position. Then the
HKS AFR a/f regulator was installed. The AFR will allow the
air-fuel ratio to be optimized for maximum power delivery. However the only
proper method to set it is still through a dyno tuning session. Fortunately the
AFR came packaged with dyno-tuning included so this nicely allowed the whole
mods package to be optimized for maximum power delivery.
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